Pumps – Condition responsive control of pump drive motor – Responsive to accumulation of pumped liquid in receiver
Reexamination Certificate
1999-07-06
2001-03-13
Walberg, Teresa (Department: 3742)
Pumps
Condition responsive control of pump drive motor
Responsive to accumulation of pumped liquid in receiver
C417S053000, C073S149000
Reexamination Certificate
active
06200101
ABSTRACT:
BACKGROUND
1. Field of Invention
This invention relates to a system for delivering pressurized liquid to an apparatus, such as a flow cytormeter, and in particular to a system having an improved liquid accumulator/pump control means for providing continuous modulation of power to a liquid pump drive means.
2. Description of Related Art
Flow cytometry apparatus has commonly used a liquid suspension of particles ensheathed in a particle-free liquid wherein this coaxial flow is passed through an analysis region and thence often to a particle sorting means. Such coaxial flow systems are shown in an article by P. J. Crossland-Taylor, Nature 171, 37 (1953) and in U.S. Pat. No. 3,826,364, which are hereby referred to and incorporated herein. Sheath liquid is usually a phosphate buffered saline solution and is usually supplied to the analysis region from a closed reservoir pressurized by air from an air pressure regulator connected to a source of air at higher pressure (note items 16, 26, and 22 of U.S. Pat. No. 3,826,364). Since particle analyzers and particle sorters often depend on consistent liquid flow velocities through the analysis region, this air pressurized sheath supply system has the following shortcomings:
1) As the sheath supply reservoir empties during operation of the flow cytometer the liquid level decreases and the loss of head causes a decrease in liquid flow rate;
2) Changes in sheath liquid temperature cause changes in sheath liquid flow rate due to changes in liquid viscosity. Changes in liquid temperature can result from changing ambient air temperature or from sheath reservoir replenishment with liquid at a different temperature.
3) Replenishment of sheath liquid is inconvenient, requiring stopping operation of the flow cytometer, de-pressurizing the reservoir, opening and refilling the reservoir, re-pressurizing the reservoir and restarting the flow cytometer;
4) The pressurized reservoir has often been a stainless steel ASME pressure vessel which is both expensive and unsuitable for visual observation of liquid level in the reservoir;
5) Air dissolves in the sheath liquid in time and can later be released as bubbles as the liquid loses pressure while flowing through filters, valves, and conduits to the analysis and sorting regions. Bubbles in these regions often prevent proper analysis or sorting functions; and
6) When pressureized air supply is not available at a flow cytometer installation, then a separate air compressor, motor, reservoir, and controls must be provided.
Attempts to use gear or centrifugal pumps to pressurize sheath liquid, usually phosphate buffered saline, have not produced practical designs. Neither pump is inherently self-priming so initial start up or restart after running out of liquid requires the operator to perform special procedures such as bleeding air from the system. If either pump is kept running when liquid flow through the flow cytometer stops, then the pump will tend to overheat and be damaged. Solutions such as an overflow/overpressure line for returning pressurized liquid back to the supply reservoir or stopping the pump add cost and complexity. Also gear and centrigugal pumps suitable for long life operating with corrosive saline are expensive.
Many of these shortcomings of gear or centrifugal pumps are avoided by diaphragm pumps, particularly those with polymer housings and with elastomer diaphragms and check valves. However, diaphragm pumps require a liquid accumulator to supply pressurized liquid during the refilling stroke of the pump. Common accumulators employ a piston loaded by a spring or a bladder loaded by compressed gas or combinations thereof (as is shown in U.S. Pat. No. 4,278,403. This patent shows an accumulator
35
which operates a pump P via a switch
43
in an on/off mode from a pressure movable partition element, piston
36
. This on/off mode of pump control with its dead band between On and Off conditions results in significant changes in pressure in accumulator
35
. In addition the friction from seals for piston
36
and stem
41
produce inaccuracies in the sensing of pressure in accumulator
35
. Also these seals are subject to wear and leakage which limit the durability of accumulator
35
.
OBJECTS AND ADVANTAGES
Accordingly several objects and advantages of my invention are:
a) to provide essentially pulse-free constant pressure liquid to an apparatus, such as a flow cytometer, unaffected by liquid level changes in the supply reservoir;
b) to employ an unpressurized supply reservoir which is easy to refill, is simple and low cost, may be raised and lowered without affecting the liquid supply pressure, does not introduce air into the sheath liquid, does not require a separate air supply and valves, may be sized large to reduce replenishment frequency, may be transparent for visual observation of liquid level, and may be replenished without stopping operation of the apparatus;
c) to provide for manual or automatic adjustment of the sheath liquid pressure as required to compensate for variations in sheath liquid temperature and thereby maintain sheath liquid flow rate substantially constant and thus maintain critical flow cytometer timing such as:
Particle transit time from laser beam to drop break-off for drop-in-air sorters,
Particle transit time from laser beam to catcher tube for a catcher tube sorter;
Particle transit time between laser beams in a multiple laser analyzer or sorter;
d) to provide a novel liquid accumulator which can accept the liquid volume delivered by one stroke of a diaphragm pump with negligble change in liquid pressure; and
e) to provide a self-priming pump in a liquid supply system where the liquid contacts only non-metal parts thus avoiding metal corrosion and contamination of the liquid.
Other objects and advantages are to provide apparatus and method for delivering pressurized liquid to an apparatus which is small, simple, low cost, reliable, durable, quiet, accurate, essentially pulse-free, and which operates with low electric power.
SUMMARY OF THE INVENTION
The present invention is directed to a pulse-free, constant pressure liquid delivery system which may be adapted for connection to an apparatus, such as a flow cytometer. Preferred embodiments of the invention provide for manual or automatic adjustment of the liquid pressure to compensate for variations in liquid supply temperature and thus maintain constant liquid flow rate through the apparatus. This invention avoids many of the problems, inconveniences, and cost associated with other liquid supply systems by use of a novel liquid accumulator design and an electric motor driven reciprocating diaphram pump controlled by a simple electronic control responsive to the liquid volume in the accumulator.
REFERENCES:
patent: 3349785 (1967-10-01), Duffy
patent: 3738776 (1973-06-01), Debare
patent: 3937596 (1976-02-01), Braidwood
patent: 3958898 (1976-05-01), Abrahams
patent: 3969035 (1976-07-01), Silbernagel
patent: 3975115 (1976-08-01), Fisher
patent: 5213477 (1993-05-01), Watanabe
patent: 5315867 (1994-05-01), Hartel
patent: 5336054 (1994-08-01), Seah
patent: 5425624 (1995-06-01), Williams
patent: 5672050 (1997-09-01), Webber
patent: 5777221 (1998-07-01), Murthy
patent: 5915925 (1999-06-01), North, Jr.
patent: 6017194 (2000-01-01), North, Jr.
Campbell Thor
Walberg Teresa
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